The Federal Information Processing Standard (FIPS) Publication 140-2, (FIPS PUB
140-2), titled "Security Requirements for Cryptographic Modules" is a U.S.
government computer security standard used to approve cryptographic modules.
Elasticsearch offers a FIPS 140-2 compliant mode and as such can run in a FIPS 140-2
enabled JVM. In order to set Elasticsearch in fips mode, you must set the
xpack.security.fips_mode.enabled to true in elasticsearch.yml

For Elasticsearch, adherence to FIPS 140-2 is ensured by

Using FIPS approved / NIST recommended cryptographic algorithms.

Delegating the implementation of these cryptographic algorithms to a NIST
validated cryptographic module (available via the Java Security Provider
in use in the JVM).

Allowing the configuration of Elasticsearch in a FIPS 140-2 compliant manner, as
documented below.

If you plan to upgrade your existing Cluster to a version that can be run in
a FIPS 140-2 enabled JVM, the suggested approach is to first perform a rolling
upgrade to the new version in your existing JVM and perform all necessary
configuration changes in preparation for running in fips mode. You can then
perform a rolling restart of the nodes, this time starting each node in the FIPS
140-2 JVM. This will allow Elasticsearch to take care of a couple of things automatically for you:

Secure Settings will be upgraded to the latest format version as
previous format versions cannot be loaded in a FIPS 140-2 JVM.

Self-generated trial licenses will be upgraded to the latest format that
is compliant with FIPS 140-2.

If you are on a appropriate license level (platinum) you can elect to perform
a rolling upgrade while at the same time running each upgraded node in a
FIPS 140-2 JVM. In this case, you would need to also regenerate your
elasticsearch.keystore and migrate all secure settings to it, in addition to the
necessary configuration changes outlined below, before starting each node.

Apart from setting xpack.security.fips_mode.enabled, a number of security
related settings need to be configured accordingly in order to be compliant
and able to run Elasticsearch successfully in a FIPS 140-2 enabled JVM.

The use of TLS ciphers is mainly governed by the relevant crypto module
(the FIPS Approved Security Provider that your JVM uses). All the ciphers that
are configured by default in Elasticsearch are FIPS 140-2 compliant and as such can be
used in a FIPS 140-2 JVM. (see xpack.ssl.cipher_suites)

Keystores can be used in a number of Default TLS/SSL settingsedit in order to
conveniently store key and trust material. Neither JKS, nor PKCS#12 keystores
can be used in a FIPS 140-2 enabled JVM however, so you must refrain from using
these keystores. Your FIPS 140-2 provider may provide a compliant keystore that
can be used or you can use PEM encoded files. To use PEM encoded key material,
you can use the relevant \*.key and *.certificate configuration
options, and for trust material you can use *.certificate_authorities.

FIPS 140-2 compliance dictates that the length of the public keys used for TLS
must correspond to the strength of the symmetric key algorithm in use in TLS.
Depending on the value of xpack.ssl.cipher_suites that
you select to use, the TLS keys must have corresponding length according to
the following table:

Elasticsearch offers a number of algorithms for securely hashing credentials in memory and
on disk. However, only the PBKDF2 family of algorithms is compliant with FIPS
140-2 for password hashing. You must set the the cache.hash_algo realm settings
and the xpack.security.authc.password_hashing.algorithm setting to one of the
available PBKDF2 values.
See User cache and password hash algorithmsedit.

Password hashing configuration changes are not retroactive so the stored hashed
credentials of existing users of the file and native realms will not be updated
on disk.
Authentication will still work, but in order to ensure FIPS 140-2 compliance,
you would need to recreate users or change their password using the
elasticsearch-user CLI tool for the file realm and the
User Management APIs for the native realm.

The user cache will be emptied upon node restart, so any existing hashes using
non-compliant algorithms will be discarded and the new ones will be created
using the compliant PBKDF2 algorithm you have selected.

Due to the limitations that FIPS 140-2 compliance enforces, a small number of
features are not available while running in fips mode. The list is as follows:

Azure Classic Discovery Plugin

Ingest Attachment Plugin

The elasticsearch-certutil tool. However,
elasticsearch-certutil can very well be used in a non FIPS 140-2
enabled JVM (pointing JAVA_HOME environment variable to a different java
installation) in order to generate the keys and certificates that
can be later used in the FIPS 140-2 enabled JVM.

The elasticsearch-plugin tool. Accordingly, elasticsearch-plugin can be
used with a different (non FIPS 140-2 enabled) Java installation if
available.

The SQL CLI client cannot run in a FIPS 140-2 enabled JVM while using
TLS for transport security or PKI for client authentication.